Peptide uptake is the process by which individual cells are able to transport intact peptides across their plasma membranes. The process is a general physiological phenomenon of bacteria, fungi, plant cells and mammalian cells (Becker, J. M. et al., In: Microorganisms and Nitrogen Sources, Payne, J. W. (ed.), John Wiley and Sons, Inc., pp. 257-279 (1980); Matthews, D. M. et al., Curr. Top. Membr. Transp. 14:331-425 (1980)). In every case studied so far, peptide transport is a specific biochemical process in which small peptides (.ltoreq.6 amino acids) are transported across a membrane by energy-dependent, saturable carriers.
Three genetically distinct systems of peptide uptake have been identified in gram-negative bacteria. An oligopeptide permease (Opp) system has been identified in bacteria such as E. coli, and S. typhimurium (Andrews, J. C. et al., J. Bacteriol. 767:484-492 (1985); Hogarth, B. G. et al., J. Bacteriol. 753:1548-1551 (1983)). The Opp system is capable of transporting peptides having up to 5 aimino acid residues, regardless of their side chains (Payne, J. W. et al., J. Biol. Chem. 243:3395-3403 (1968); Payne, J. W. et al., J. Biol. Chem. 243:6291-6299 (1968)). In contrast, tripeptide permease (Tpp) systems, such as that of S. typhimurium, exhibit an apparent affinity for peptides having hydrophobic amino acid residues (Gibson, M. M. et al., J. Bacteriol. 760:122-130 (1984)). The third system, a dipetide permease (Dpp) system, has a preference for transporting dipeptides (Abouhamad, W. N., et al., Mol. Microbiol. 5:1035-1047 (1991)). Functionally similar systems have been described in fungi and yeast (Naider, F. et al., In: Current Topics in Medial Mycology, volume II, McGinnis, M. M. (ed.) (1987)), but have not been well characterized.
The genes that encode the protein components of the oligopeptide transporters of E. coli (Kashiwagi, K. et al., J. Biol. Chem. 265:8387-8391(1990)), Salmonella typhimurium (Hiles, I. D. et al., Eur. J. Biochem. 158:561-567 (1986); Hiles, I. D. et al., J. Molec. Biol 195:125-142 (1987)), Bacillus subtilis (Rudner, D. Z. et al., J. Bacteriol. 173:1388-1398 (1991); Perego, M. et al., Mol. Microbiol. 5:173-185 (1991)), Streptococcus pneumoniae (Alloing, G. et al., Mol. Microbiol. 4:633-644 1990)), and Lactococcus lactis as well as two dipeptide permeases, one in E. coli (Abouhamad, W. N., et al., Mol. Microbiol. 5:1035-1047 (1991)), and the other in Bacillus subtilis (Mathiopoulos, C. et al., Mol. Microbiol. 5:1903-1913 (1991)) have been cloned and sequenced.
The ability of bacteria and plant cells to accumulate peptides has been found to be dependent upon peptide transport systems (Becker, J. M. et al., In: Microorganisms and Nitrogen Sources, Payne, J. W. (ed.), John Wiley and Sons, Inc., pp. 257-279 (1980); Matthews, D. M. et al., Curr. Top. Membr. Transp. 14:331-425 (1980); Higgins, C. F. et al., In: Microorganisms and Nitrogen Sources, Payne, J. W. (ed.), John Wiley and Sons, Inc., pp. 211-256 (1980); Naider, F. et al., In: Current Topics in Medial Mycology, volume II, McGinnis, M. M. (ed.) (1987)). These systems are distinct from the mechanisms that mediate the uptake of amino acids.
The existence of peptide transport systems in plants was demonstrated by showing that plants could accumulate non-hydrolyzable, non-physiological peptide substrates, intact and against a concentration gradient (Higgins, C. F. et al., Planta 134:205-206 (1977); Higgins, C. F. et al., Planta 136:71-76 (1977); Higgins, C. F. et al., Planta 138:211-216 (1978); Higgins, C. F. et al., Planta 142:299-305 (1978); Sopanen, T. et al., FEBS Lett. 79:4-7 (1977)). The transport system was found to exhibit saturation kinetics and to be inhibited by a range of metabolic inhibitors (Higgins, C. F. et al., Planta 136:71-76 (1977)). The plant peptide transport system can transport both di- and tripeptides (Sopanen, T. et al., FEBS Lett. 79:4-7 (1977); Higgins, C. F. et al., Planta 142:299-305 (1978)). Plant peptide transport systems are capable of transporting a wide variety of peptides. These systems exhibit broad transport specificity with respect to amino acid side-chains. The presence of D-amino acids, however, reduces the transport rate, thus indicating that the transporters have strong stereo specificity. Two proteins, approximately 66 D and 41 D, have been suggested as components of the plant peptide transport system in barley grains (Payne, J. W. et al., Planta 170:263-271 (1987).
The primary function of peptide transport is to supply amino acids for nitrogen nutrition (Payne, J. W. et al., In: Microorganisms and Nitrogen Sources, Payne, J. W. (ed.), John Wiley and Sons, Inc., pp. 257-279 (1980); Matthews, D. M. et al., Curr. Top. Membr. Transp. 14:331-425 (1980); Becker, J. M. et al., In: Microorganisms and Nitrogen Sources, Payne, J. W. (ed.), John Wiley and Sons, Inc., pp. 257-279 (1980); Adibi, S. A. et al., Metabolism 36:1001-1011 (1987); Higgins, C. F. et al., Planta 138:211-216 (1978); Sopanen, T. et al., FEBS Lett. 79:4-7 (1977); Higgins, C. F. et al., Planta 138:217-221 (1978)). In bacteria, peptide transport has, however, also been associated with sporulation (Perego, M. et al., Mol. Microbiol. 5:173-185 (1991); Mathiopoulos, C. et al., Mol. Microbiol. 5:1903-1913 (1991)); chemotaxis (Manson, M. D. et al., Nature 321:253-256 (1986), and the recycling of cell wall peptides (Goodell, E. W. et al., J. Bacteriol 169:3861-3865 (1987)).
A variety of plant pathogens attack plants by secreting toxic peptides. A capacity to control peptide transport may permit the development of pathogen-resistant plants. The present invention provides polynucleotide molecules, and methods that may be useful for producing such valuable plants.